A) Field of the invention
The present invention relates to a capping board of improved structure, which comprises at least one sheet of electrically conductive material embedded therein.
B) Brief Description of the Prior Art
In the hydrometallurgical industry, it is of common practice to refine metal by electrolysis in electrolytic cells especially designed for this purpose. The metals to be refined are usually conventional metals like copper, zinc, nickel or cadmium, or precious metals like silver, platinum or gold, and others.
In the commonly used hydrometallurgical process, metal plates are used as anodes or cathodes or both. These metal plates weight several hundred pounds. Usually, the metal to be refined, or the metal used to carry the electric current, is in the form of plates of a given thickness, which are provided at their upper end with two laterally extending projections. Such projections facilitate gripping, handling and hanging of the plates on lateral sidewalls of the cells. They also facilitate other operations.
In use, the plates which as aforesaid can each weight several hundred pounds, are immersed into the cells in parallel relationship and are used as anodes, cathodes or both, depending on the affinity of the metal being refined.
In order to have the electrodes positioned at the exact place, it is of common practice to place a member, called “capping board”, onto the top surface of each lateral sidewall of the cells. Such capping boards are used to position the plates with respect to each other. Some of them are also used as electric insulators between adjacent cells and/or each electrodes and/or the ground.
In practice, the capping boards are used not only as supports to position the electrodes, but also as supports to avoid damage to the masonry or concrete forming the lateral side walls of the cells during the insertion and removal of the heaving electrodes.
As examples of such capping boards and the way they can be manufactured, reference can be made to U.S. Pat. No. 4,213,842 issued on Jul. 22, 1980 and Canadian patent No. 1,102,737 issued on Jun. 9, 1981 both in the name of Jean L. DUFRESNE and to the U.S. Pat. No. 5,645,701 issued on Jul. 8, 1997 and Canadian laid-open patent application No. 2,171,412 filed on Mar. 8, 1996 both in the names of Jean L. DUFRESNE and the present inventor, namely, Robert P. DUFRESNE.
As other examples of such capping boards, reference can also be made to U.S. Pat. No. 3,697,404 issued on Oct. 10, 1972 to Peter M. PAIGE and to U.S. Pat. No. 6,342,136 issued on Jan. 29, 2002 to OUTOKUMPU OYJ.
Thus, as aforesaid, in order to electrodes of electrolytic cells at proper locations within the cells it is of common practice to use insulating capping boards which have the advantages of holding the electrodes at very precise positions while being in contact with at least one current supply contact bar or to be insulated from the same. Thus, the combined use of capping boards and current supply contact bars have the particularity of allowing insulation and distribution of electric current at the same time.
In practice, to achieve proper electrical contact with a contact bar or insulation from the same, the plates forming the electrodes are provided with support hanging legs externally projecting on their opposite upper ends.
In practice also, only one of the legs of each plate is intended to be in contact with a current supply contact bar. The other leg of the same plate thus has to be held onto the capping board in such a way as to be insulated. Thus, the capping board per se plays the role of an insulator and has, for this purpose, to be made of material that are insulating.
If such has proved to be sufficient, there are still some problems with the existing systems using of capping boards with one or more supply bars placed on their top surfaces.
One of these problems is due to short circuits occurring during the hydrometallurgical operation of the electrolysis or electro-winning process. Other problems are also due to poor repartition of the electric current density distribution.
As shown in the above mentioned U.S. Pat. Nos. 3,697,404 and 6,342,136, the contact bars which can be V-shaped, have sharp edges and/or corrugated surfaces that may wear the surface of the insulating capping board. Such may in time substantially decrease the lifetime of the capping board and causes short circuit.
When short circuits arise, the temperature of the metal plates forming the electrode increases. This increase of temperature is transmitted by the metal plates to the insulating capping-board, which, as aforesaid, are made of insulating organic material which are very weak to thermal resistance especially in view of high pressure created by the such heavy weight metal plates.
Independently of the above, the combination of this high temperature and pressure as it occurs in use in the hydrometallurgical process, actually creates deformation within the capping boards. Such deformation is unacceptable since it may generate short circuits that may propagate from one cell to another cell.
These short circuits may produce a refined metal with major impurity and defects that gives to the quality of the refined metal a poor quality to be rejected.